1. Field of the Invention
This invention relates to control mechanisms having angularly adjustable shafts, and, more particularly, relates to devices which permit adjustment of an adjustable control mechanism only upon disengagement of a locking structure associated with the device.
2. Description of the Prior Art
There are many different types of control mechanisms having angularly adjustable output shafts. One such mechanism is the well-known potentiometer. A potentiometer is a variable resistor or rheostat. Potentiometers are commonly used to control electrical devices, such as volume and other controls on audio equipment. Potentiometers comprise a resistive element, a sliding contact (wiper) that moves along the element, making electrical contacts with one part of it, electrical terminals, a housing containing the element and wiper, and an output shaft with which the wiper can be moved from one end of the element to the other. Potentiometer output shafts come in all different configurations, e.g. splined, D-shaped cross-section, hexagonal, or any other polygonal shape.
In many, if not most, potentiometers applications, the angular position of the output shaft is manually set by a user. The user wishes for the angular position of the output shaft to remain in a desired position, so that he or she will not have to re-set that position each time the piece of the equipment that the potentiometer controls is moved, as the perfected settings for such knobs typically takes a long time to achieve.
Potentiometers on consumer audio equipment employ knobs to make it easier to adjust the setting of the potentiometer, to allow for indicia or other markings to be used to indicate setting levels and to provide an esthetic element.
In the case of audio equipment, potentiometers are widely used to adjust the level of analog signals present in the various electronic circuits in the device. As but one example, musicians experience significant disruptions and inconveniences when potentiometer knobs are accidentally bumped during transportation of audio equipment, requiring re-setting and/or re-calibration of the equipment each time it is used.
Control knobs which are normally out of engagement with the output shaft of the mechanism to be adjusted have been proposed. Such knobs exert a manual force on the knob to cause the knob to engage some apparatus to affect turning of the shaft. Such an arrangement would not only be cumbersome to use with consumer audio equipment, but is still susceptible of inadvertent mis-adjustment from accidental bumping, because bumping into such a device exerts a force on the knob, which could cause the locking mechanism to engage and change the adjustment of the output shaft.
Some minimal efforts have been directed in the past to address the problem inherent in adjustable potentiometer output shafts/knobs, namely that they are easily knocked out of adjustment by incidental contact, and the inconvenience and frustration resulting therefrom. For example, U.S. Pat. No. 2,899,844 to Melloy discloses a controlled knob for an adjustable kitchen timer adapted to prevent rotation of the output shaft of the timer in one direction so as to avoid damage to the timer. Melloy discloses a cooperating locking element which only prevent rotation of the knob in one direction, such that inadvertent rotation of the knob can occur in the opposite direction.
The following patents disclose control knobs which when pushed down upon, permit rotation of the potentiometer output shaft and are, for various reasons, undesirable solutions to the problem discussed above; U.S. Pat. No. 4,779,305 to Gorsek; U.S. Pat. No. 5,513,831 to Seward and U.S. Pat. No. 6,696,915 to Pan.
Another type of locking knob is disclosed in U.S. Pat. No. 5,152,187 to LaFemina, which comprises a knob slightably disposed on a splined output shaft and movable between a first, locked position in which corresponding locking elements on the underside of the knob and connected to the potentiometer and/or housing are lockingly engaged, and a second, adjustment, position in which the locking members are disengaged from each other, such that the knob and output shaft can be annularly adjusted. However, the knob of LaFemina is not retained relative to the output shaft while in the second position, such that it can easily be slid off of the output shaft.